Preheat your oven to 350°F (175°C) and prepare a cupcake pan by lining it with 12 cupcake liners.

In a large mixing bowl, beat the softened unsalted butter and granulated white sugar together until the mixture is fluffy and pale, about 1-2 minutes.

Add in one room-temperature egg, one egg yolk, and the vanilla extract to the butter-sugar mixture. Mix until smooth and well combined, approximately 1 minute.

Add room-temperature whole milk, sour cream, and canned pumpkin puree into your wet ingredients. Mix until thoroughly incorporated.

In a separate bowl, whisk together the sifted all-purpose flour, black cocoa powder, pumpkin pie spice, baking powder, baking soda, and salt.

Gradually add the dry ingredients to the wet mixture, stirring gently until just combined and smooth.

Divide the cupcake batter evenly among the lined cupcake cups, filling each about 3/4 full. Bake for 17-19 minutes, or until a toothpick comes out clean.

Allow the cupcakes to cool in the pan for about 5 minutes before transferring them to a wire rack.

Spread pumpkin puree on a paper towel to dry out excess moisture until it reduces to 1/4 cup for the frosting.

In a medium bowl, beat the softened unsalted butter until pale and fluffy, roughly 5-10 minutes.

Mix in the cold cream cheese and the dried pumpkin puree to the creamed butter, adding pumpkin pie spice and blend until smooth.

Gradually add the sifted powdered sugar, mixing until the frosting is light and fluffy.

Transfer the cream cheese frosting into a piping bag and pipe it generously over the cooled cupcakes.